1. Field of the Invention
The present invention relates to a rare earth permanent magnet.
2. Description of the Related Art
Ferrite sintered magnets have been conventionally used as magnets for high-speed rotating motors. In accordance with demand in higher performance, however, motors using rare earth permanent magnets instead of the ferrite sintered magnets are widely used these days.
In recent years, a rotation speed tends to further increase in accordance with higher efficiency of the motors, and a field weakening control method is commonly applied for controlling the motors.
In the above two cases, a large eddy current flows through the magnet. A rare earth sintered magnet has an electric resistance that is smaller than an electric resistance of the ferrite sintered magnet. Thus, it is known that a large eddy current flows in case of using a rare earth sintered magnet for the motor, and that this magnet is demagnetized due to heat generated by the eddy current.
Patent Document 1 discloses a method for preventing an eddy current by dividing a rare earth sintered magnet and coating its entire surface with resin as insulation treatment.
Patent Document 1: JP 2003-134750 A